Onboard automatic tire inflation systems are currently available for use on trucks and other vehicles. Such systems have been successfully used in non-powered vehicle axle assemblies (i.e., the axle assemblies of trucks or other vehicles which do not include powered drive shafts linked to the vehicle differential or other drive system) to deliver make-up air to a vehicle tire in the event that the tire is punctured or begins to leak for other reasons.
By way of example, an onboard system for maintaining a predetermined pressure in each of the tires of a non-powered truck tandem axle assembly is currently available from Airgo, Inc. of Edmond, Okla. The Airgo unit includes a tire inflation system which delivers compressed air from an onboard compressor (e.g., the compressor used for supplying air to the truck brakes) to the interior of the tandem axle, or to a tube extending through the axle, in the event that a leak occurs in any of the four tandem axle tires. The Airgo unit also includes: a pair of rotary seals provided proximate the outer ends of the non-powered tandem axle; a set of air lines extending from the rotary seals for delivering air from the interior of the axle, through the rotary seals, to each of the four tires; check valves provided in the air lines for preventing reverse air flow from the tires to the axle; and an indicator light which alerts the operator that a leak has developed. The system controls the make-up air flow in accordance with the operating pressure required by the tires. For most tandem truck axles, the automatic inflation system will typically be operable for providing a sufficient make-up air flow to maintain a tire pressure of at least 90 psig and more preferably at least 95 psig. An onboard automatic inflation system of this type is described, for example, in U.S. Pat. No. 6,105,645, the entire disclosure of which is incorporated herein by reference.
Although the rotary union employed in the Airgo system allows the use of onboard automatic tire inflation systems in non-powered axle assemblies, the development of a commercially viable system which would allow the use of such onboard automatic tire inflation systems in the powered drive axle assemblies of trucks and other vehicles has been problematic. We are not aware of any commercially viable systems which are currently in use for drive axle tire inflation for on-road trucks. Moreover, the available drive axle systems usable on other types of vehicles have significant shortcomings and disadvantages. For example, such systems (a) will typically inflate only during a portion of the revolution of the tire or only when the vehicle is stationary, (b) cannot operate at highway speeds, (c) do not provide continuous seal lubrication, (d) are not self contained, and/or (e) require external components which do not fit with the existing axle assembly.
Consequently, a need presently exists for a commercially viable device which will address and overcome these problems and limitations and will allow a flow of make-up air from an onboard tire inflation system to be automatically delivered through a drive axle assembly. Such device preferably will not interfere with the operation of the drive axle assembly and will preferably also be compatible for use with existing onboard automatic tire inflation systems. Further, the device will preferably be readily adaptable for use in two-wheel drive axle systems or in truck tandem axle systems having a pair of tandem wheels and tires mounted on each end thereof.